#include <iostream>
using namespace std;
// first name space
namespace first_space{
    void func(){
        cout << "inside first_space" << endl;
    }
}
namespace second_space{
    void func(){
        cout << "inside second_space" << endl;
    }
}
int main(){
    first_space::func();
    second_space::func();
    return 0;
}
// namespace 用于区分不同库中可用的相同名称的类似函数，类，变量等
// 命名空间定义了范围
